| Three-dimensional graphene could be formed by graphene sheets, it retained graphene excellent physical and chemical properties, and its three-dimensional structure also gave its many superior characteristics, such as large surface area, porous structure, etc. Thus, three-dimensional graphene had more advantages in terms of mass transfer and loading catalyst. In this study, three-dimensional graphene and its composites could be synthesis by a simple method, and their properties were characterized. The adsorption and degradation of materials were investigated. The main contents of this study were:1. Preparation and characterization of three-dimensional graphene:Graphene oxide was made by modified Hummers’method, three-dimensional graphene was formed by the reduction of graphene oxide. The three-graphene was characterized by scanning electron microscope, X-ray photoelectron spectroscopy analysis, X-ray diffraction and N2 adsorption-desorption experiments. The results proved that three-dimensional graphene was porous structure, majority of the surface oxygen-containing functional groups were removed, the specific surface area of it was 211.5m2/g and its pore size was 4.309nm.2. The adsorption and electrosorption behaviors of three-dimensional graphene: The electrosorption isotherm experiments data of dyes by three-dimensional graphene were fit well by Freundlich model. In kinetic experiments, the adsorption and electrosorption data of dyes were fit well by pseudo-second-order model. For the negatively charged dyes, Acid red 88 and Orange II, the electrosorption rates of these increased with the increase of voltage. For the positively charged dye, Methylene Blue had the same rule. The dyes adsorbed on the surface of the three-dimensional graphene could not desorb by applying the same electrical polarity with dyes, probably because the electrostatic repulsion generated by the applied voltage did not reach a degree to overcome π-π bonding, van der Waals force, etc.3. The results of DFT-D model showed that after dyes adsorbed on the surface of three-dimensional graphene, dyes molecules and graphene sheet could occur different degrees of bend. The dipole moment of three-dimensional graphene changed after dyes adsorbed, the change of polarization could influence the properties of ekectron transfer and conductiove performance.4. Preparation and characterization of three-dimensional graphene/MnO2 composites:The composites were synthesized by deposition method in situ, and we used many means to characterize the composites. The results showed that MnO2 were loaded on the surface of three-dimensional graphene successfully in the form of nanostructure5. The removal behaviors of Tetracycline by three-dimensional graphene/MnO2 composites:By comparison test, the composites were preferably in the removal of tetracycline, because the three-dimensional graphene solved the problem of MnO2, and graphene had the high conductivity. The removal experiments of tetracycline by composites conformed Rate-retarded model, mainly due to Mn2+ produced by reaction and the composites of tetracycline and Mn adsorbed on the surface of three-dimensional graphene/MnO2 composites, reducing the reactive sites of composites. The larger the initial concentrations of tetracycline were, the faster the rates of reaction were. The reaction is endothermic, therefore the high temperature was benefit to removal of tetracycline. The greater the electrostatic repulsion between the composite and tetracycline at high pH caused that the removal of tetracycline reduced. With the increase of concentrations of Mn2+and Na+, the inhibition on the removal of tetracycline was more obvious, Mn2+ at low concentration had the inhibition, because Mn2+ could adsorb on the surface of MnO2 specifically, occupying the reactive sites. However, Na+ occupied Mn4+ vacancy site, but did not react with Mn4+. |
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